Keithley 6521, Instruction Manual, Page: 51 / 65

Service Information
4-9
4.6.3 Troubleshooting procedure
Table 4-3 summarizes scanner card troubleshooting steps.
Refer to the schematic diagrams and component layout
drawings at the end of Section 5 for component locations.
WARNING
Lethal voltages are present within the
Model 6517. Some of the procedures
may expose you to hazardous voltages.
Observe standard safety precautions for
dealing with live circuits. Failure to do
so could result in personal injury or
death.
CAUTION
Observe the following precautions when
troubleshooting or repairing the switch
card:
• To avoid contamination, which could
degrade card performance, always
handle the card only by the side
edges. Do not touch edge connectors,
board surfaces, or components on the
card. Also, do not touch areas
adjacent to electrical contacts on
connectors.
• Use care when removing relays from
the PC board to avoid pulling traces
away from the circuit board. Before
attempting to remove a relay, use an
appropriate de-soldering tool to clear
each mounting hole completely free
of solder. Each relay pin must be free
to move in its mounting hole before
removal. Also, make certain that no
burrs are present on the ends of the
relay pins.
4.6 Troubleshooting
4.6.1 Troubleshooting equipment
Table 4-2 summarizes recommended equipment for trouble-
shooting the Model 6521/6522.
4.6.2 Troubleshooting access
In order to gain access to the scanner card circuit board to
measure voltages under actual operation conditions, perform
the following steps:
1. Turn off the Model 6517 power, and disconnect the line
cord and all other equipment.
WARNING
Disconnect the line core and all other
equipment from the Model 6517 and the
scanner card before removing the cover.
2. If cables are connected to the scanner card, remove the
scanner card from the electrometer.
3. Remove the Model 6517 cover.
4. Install the scanner card in the electrometer.
5. Disconnect any cables connected to the scanner card
input/output jacks.
6. Connect the line cord, and turn on the power to measure
voltages (see following paragraph).
Table 4-2
Recommended troubleshooting equipment
Description
Manufacturer/
Model
Application
Multimeter
Oscilloscope
Keithley 2001
TEK 2243
DCV checks
View logic waveforms